1. Field of the Invention
The invention relates to the impact resistant structures for transparent, translucent and similar panes, for example in or around doors and windows.
According to the invention, a pane structure comprises a laminate with a flexible plastic sheet that protrudes beyond a rigid body, for example the flexible plastic center sheet of a glass-plastic-glass laminate. The protruding sheet of plastic remains in a plane and is spaced from one or both of the facing surfaces of the pane, e.g., by a thickness of glass. The pane fits in an inset in a wall or panel, which can be formed by a stepped cutout, or can be limited by an affixed molding or strip. The inset is substantially as deep as the spacing, such that the plastic sheet is positioned to protrude for a distance adjacent to the inset where the pane is fitted. The protruding plastic is coplanar with the integral portion of the plastic in the laminate and is clamped by molding elements to the surface adjacent to the inset. In this way the pane is rigidly fixed in the inset so long as the pane remains intact, is resiliently fixed in the opening in any event, and can be replaced readily if broken.
2. Prior Art
Efforts have been made for some years to improve the structural strength of elements of buildings, particularly in coastal areas and most particularly in the state of Florida after unexpectedly heavy damage was caused by a hurricane in 1992. Standards were developed for determining the merits of structures for withstanding damage in storms characterized by high winds, such as hurricanes and tornadoes. In such storms, wind pressure imposes static and also dynamic or cyclic loads on structures. Strong winds also entrain debris that may strike structures with considerable force.
An impact from fast moving debris can cause a structure such as a window or door to fail. Failure of a window or door potentially weakens the structure as a whole, and at least increases the likelihood of further damage by permitting wind, rain and possibly additional debris to enter the building. Conventional window glass is readily frangible (i.e., not tempered or laminated safety glass). Thus breaking the glass may leave an unobstructed opening.
After incidents of hurricane damage, more stringent building code standards were applied in coastal areas to deal with this danger. Among other requirements, windows, doors and other similar openings were required to be capable of surviving certain impacts without failing to the extent that the opening that they occupy becomes breached. Thus for example, the glass in a window or door might fracture and the window (etc.) could still meet the code, provided that the manner of breakage kept intact the envelope of the building structure.
Preventing any fracture of the glass might require glass that is very strong. Glass can be made strong enough even to be xe2x80x9cbulletproof,xe2x80x9d but there are drawbacks. The glass might be very thick and aesthetically undesirable, noticeably refractive, less-than transparent, unduly heavy, expensive, etc. The code requirement to keep intact the building envelope in the event of impact is usually met instead by using laminated safety glass, similar to glass used in automobiles. The glass is a sandwich of frangible glass attached to a flexible plastic sheet. The glass can fracture but remains affixed to the flexible sheet. The flexible sheet and the pieces of glass that remain adhered to the plastic, maintain a barrier across the opening, even if the glass becomes fractured. The pane may have to be replaced if the glass fractures, but hurricanes and associate breakage are rare, so the cost/benefit mix is right.
The specific standards applicable in South Florida and other jurisdictions are different in different counties, but typically divide a building into zones of different elevation. At low elevation up to 10 m (30 ft) of building elevation, relatively large wind-borne debris might be expected, e.g., trashcans, lawn furniture, vegetation, fencing and building elements, etc. At higher elevation, smaller debris is more likely to be carried in a high wind, such as roof gravel or ballast. Either type of debris could easily break a window pane.
An exemplary standard for the xe2x80x9clarge missile zone,xe2x80x9d or low elevation zone, may require a door or window to survive test firing of a 4-kg, 0.06 m diameterxc3x971.2 m timber (substantially equal to a 9-lb framing stud) endwise at the test specimen, at a missile speed of 15 m/s (55 km/h or 50 ft/sec or 35 mph). Each test specimen is struck twice, once in the center and once in a corner. After the large missile impact tests, which may fracture the glass as discussed above, the test specimens are subjected to an extended series of many positive and negative wind pressure cycles.
Door and window structures that can routinely survive such tests are available. Some are characterized by a transparent or translucent pane that is inherently strong enough to survive an impact and is mounted rigidly in a door or wall or other structurally sound panel via a rigid mounting structure that likewise can survive the impact. Others are laminates of materials and may have layers of glass and flexible plastic, metal or fibrous mesh reinforcement, etc.
U.S. Pat. No. 5,765,325xe2x80x94DeBlock teaches a multiple layer hurricane door light construction. (A door xe2x80x9clightxe2x80x9d refers to a light transmissive pane or window installation in an otherwise opaque door or entryway or similar structure.) In DeBlock, a polycarbonate sheet having peripheral screw holes is mounted between two glass panels and is spaced from each of the glass panels. The polycarbonate sheet is rigid and relatively clear, but is much less easily shattered than glass. The door light is mounted in an opening in a door frame by means of molding members that are screwed together to clamp the door between them, and according to this patent the screws are passed through the holes around the rigid polycarbonate sheet so as to improve the structural connection between the window pane structure and the door frame. If a missile breaks the glass, the polycarbonate is likely to remain intact.
The DeBlock door light construction is less easily breached than plain glass, but the polycarbonate sheet is not attached to the glass in the manner of safety glass and instead forms only a means for improving the mechanical connection with the door via the clamping moldings. The relatively hard plain glass spaced on either side of the polycarbonate sheet normally isolates and protects the softer polycarbonate against scratches. Thus the door light appears much like a familiar glass structure. However, the multiple spaced layers of glass and polycarbonate make the door light or window relatively thick and reminiscent of bulletproof glass. The polycarbonate sheet is structurally complicated by the need for pre-formed peripheral holes, which makes the construction somewhat complicated and expensive. Safety glass can be used in the outer glass panes, but if so the safety glass does not contribute structurally to the mounting of the door light, which relies on the opposed clamping moldings and the polycarbonate sheet.
Instead of, or in addition to making a door light or window pane very durable and similar to bulletproof glass in a heavy frame, the pane can be mounted in a manner intended to absorb impact stress. Even assuming the breakage of a frangible glass portion of the door light or window, the envelope that is defined by the window can be arranged to remain intact if a flexible barrier remains in place. A partly compliant mounting reduces shock on the glass during an impact, as compared to a very rigid mounting, and reduces the incidence of breakage.
U.S. Pat. Nos. 6,101,783, Howes and 5,560,149xe2x80x94Lefevre use resilient mounting techniques that might be considered similar to mounting a rigid pane against cushioned glazing pads placed at the perimeter of the pane. In U.S. Pat. No. 5,960,606xe2x80x94Dlubak, a very heavy pane is mounted rigidly in a channel forming structure and is faced with a floating pane that does not engage in the channel, and is similarly cushioned.
In U.S. Pat. Nos. 5,937,611 and 5,777,629, both to Howes, a flexible plastic sheet or membrane is laminated into a pane assembly, for example between two outer relatively-more-rigid sheets of glass or plastic, that sandwich the flexible membrane. The flexible membrane protrudes beyond the edges of the rigid sheets and is intended to contribute to the mechanical attachment of the pane assembly to the surrounding framing.
The protruding membrane, which is flexible, can be bent or folded as desired relative to the rigid glass. In Howes ""629, a pane assembly with a protruding membrane is mounted in an opening that complements the rigid glass part. The flexible membrane is folded perpendicular to the plane of the glass pane. In a vertical window, for example, the plastic membrane on the top and bottom edges of the pane are folded into a horizontal plane and brought back toward the interior along the surface of the sill and along the underside of the header. The pane is caulked on both its inner and outer sides. A wood or vinyl frame or molding element is installed against the glass and over the protruding flexible membrane, by nails or screws or the like, extending through the molding and through the membrane, into the sill or header. The flexible membrane remains as a permanently incorporated member of the window assembly.
The same arrangements can be employed along the lateral sides of the pane as at the top and bottom. That is, the flexible membrane that protrudes laterally is brought back, perpendicular to the plane of the window pane, to reside along the inside surfaces of the side framing, where similar molding elements are attached over the membrane by fasteners extended through the molding and through the membrane into the side framing.
The membrane in the Howes ""629 patent is intended to provide an attachment that is at least somewhat compliant, by physically mounting the rigid laminated pane to the window framing via the flexible plastic sheet that is sandwiched between the glass laminate sheets and is affixed to the framing.
However, there are some problems. Howes""s structure of a plastic sheet extending outwardly in the plane of the glass is inconsistent with the need to form neat corners. The flexible membrane can be cut out at the each of the four corners, so that upper and lower flaps have vertical edges and opposite lateral side flaps have horizontal edges. Alternatively, the corners can be folded in an overlapped way, in the same way that a square package can be wrapped with flat wrapping paper. This can present problems.
One problem is that the plastic membrane does not bend easily and neatly. Bending the membrane neatly around 90 degrees all along an edge, particularly a long edge, is time consuming and needs to be done precisely. The right angle bend, as well as the flexing operations associated with achieving the bend, tend to weaken the film. If the pane is to be mounted simply in a through-opening, such as an opening in a wood or steel door body with frame or style parts having a rectangular cross section adjacent to the opening, it is necessary to resolve the problems of where the plastic film is to reside and how the plastic film is to attach structurally to the body of the door or the like, if the film is to be structurally attached at all.
A right angle folding method is possible as in Howes ""629, but after folding the membrane, mounting the pane and affixing a molding to capture the protruding plastic membrane and engage the window frame, the structural connection in Howes ""629 is possibly less than optimum. The plastic membrane is joined at a right angle to the glass sandwich, which is a stress point where the plastic may be sheared if the glass vibrates and is displaced. Panes as described are typically supplied with factory-attached frames, rather than installed at the site.
The plane of the portion of the plastic that protrudes and is folded back, according to the installation as described, perpendicular to the plane of the glass pane. Inward wind pressure on the window, which results in compression force in the plane of the flexible membrane, at least so long as the glass is intact, is not resisted. Only outward wind suction, which translates into tension in the plane of the affixed membrane, is resisted resiliently. It would be advantageous of these aspects could be improved.
The Howes ""611 patent discloses a method for making a laminated assembly comprising two glass sheets sandwiched around a flexible sheet that protrudes beyond the perimeter of the glass. The teachings of Howes ""611 are incorporated for such teachings. A first panel is laid on a flat surface. The flexible plastic sheet or membrane is laid over the pane, pulled taut, and taped to the flat surface. Double-faced adhesive tape spacers are applied around the edges and the second pane is laid atop the first pane, with the flexible sheet and the spacers in between. The other glass sheet is laid atop the flexible sheet and an adhesive is injected.
Howes ""611 discloses an alternative structural embodiment (see FIG. 2), wherein one of two laminated glass panels is longer and/or wider than the other panel. The flexible membrane extends beyond the edge of the shorter panel, but only up to the edge of the longer/wider panel. In another embodiment (FIG. 4), the flexible membrane is diverted perpendicularly as discussed above, but this structure occurs within a frame component to provide an assembled framed window element to be mounted as a unit in a window sash, door light or the like.
An arrangement as in Howes ""611 has structural benefits due to the particular modes of attachment and support between the glass and the frame structure, including the protruding flexible membrane. What is left for the designer or installer is only robustly to attach the frame component to the structural parts of a door or window frame. This is advantageous in that the installer is not required to attend to the protruding plastic membrane (which is attached to the frame component at the factory). But such a pre-manufactured frame is an expensive solution, and the entire frame must be replaced if the window is broken. It would be advantageous to provide an effective way to use a protruding membrane pane without requiring a whole pre-manufactured unit.
What is needed is an optimal impact-resistant structure, with xe2x80x9coptimalxe2x80x9d not only including ability to survive impact, but also including unit cost, replacement cost, ease of installation, attractiveness and the like. The mounting should provide a rigidly durable structural engagement for laminated panes of glass or other materials and also the resilient yet durable impact absorbing and resisting capabilities of a flexible sheet.
It is an object of the invention to provide a structure for mounting pane structures having protruding flexible membranes, whereby such pane structures can be employed without the need for special frame components.
It is another object to improve conventional pane mountings for window glass, safety glass and the like, to add an engagement structure for a resilient sheet associated with the glass.
It is a further object to provide a window structure with a complementary pane receptacle and an associated molding, wherein the molding is arranged to engage with a flexible sheet protruding beyond the pane receptacle.
It is also an object to achieve some of the advantages of pre-manufactured pane structures such as in the cited Howes patents, having flexible membranes pre-attached in frames, in a pane installation that is inexpensively and conveniently assembled at the site rather than supplied with a pre-attached frame.
These and other objects are provided by an impact resistant laminated glass and plastic pane according to the invention, for a hurricane resistant door light or similar opening. A glass pane is attached to a flexible plastic sheet that protrudes beyond the peripheral edge of the glass, preferably as an extension of the plastic laminate between outer glass laminate sheets. The pane body is mounted in a building structural part such as a door or wall, at an opening or at a recess, whereby the surface of the structural part extends up to a point adjacent to the pane. According to an inventive aspect, the flexible sheet that is attached to the pane, e.g., laminated into the pane body or otherwise attached and protruding, laps over the surface adjacent to the edge of the structural part around the pane. An elongated molding element that preferably frames the opening, is attached to the structural part so as to capture the flexible sheet between the molding element and the surface.
The structural part can be a door light opening, a window opening, a window sash, an entryway light, etc. The invention is applicable to a variety of situations and can be embodied in more or less durable and heavy ways as needed for particular sites. The structural part could be defined, for example, by a heavy solid body such as a steel door, or by a relatively lighter part such as a frame defined by a lattice of mullions. In the embodiments discussed in detail the invention is applied to the non-limiting example of a door light in an otherwise conventional hinged door.
The framed opening or mullions or the like defines a through opening or a recess. The pane is mounted in the opening at a sufficient depth to cause the flexible plastic sheet protruding from the edge of the pane to lay over a surface adjacent to the pane, over which the molding element extends. The molding element extends over the recess to mechanically clamp down on the pane, and also on the surface adjacent to the pane, thus clamping the flexible sheet against the surface. This clamping entails a force at least partly perpendicular to the plane of the pane.
In one arrangement, the protruding flexible plastic sheet is the continuous extension of the laminated plastic layer of safety glass, namely between two glass sheets attached on opposite sides of the plastic. Where just this glass-plastic-glass laminate constitutes the pane, the recess in the structural part for the pane can have a depth equal to the thickness of the inner (lower) layer of glass. This places the level of the flexible plastic at the same level as the surface of the structural part, adjacent to the opening. In such an embodiment with two glass layers at an inset, a molding element to capture both the glass and protruding plastic can have two levels defining a stepped surface. A lower or inner level clamps over the flexible plastic and attaches to the structural element by fasteners passing through the plastic. An upper one of the levels of the molding rests against the glass pane. Suitable spacers, seals and shock absorbing pads optionally can be placed between the parts.
In other embodiments the glass can have additional parts such as a spacer between glass and/or plastic layers to provide an air gap. Another embodiment discussed below comprises molding strips affixed from opposite sides of a straight through-opening, wherein a molding part attached from one side is dimensioned to form an inset of the required depth on the opposite side, clamping simultaneously the pane and the door structure adjacent to the through opening.
A preferred exemplary molding element comprises an aluminum extrusion and can have elongated grooves or lips to engage securely with the flexible plastic. On the laterally outer sides of the molding, catch lips are raised. A molding cover with inwardly facing catch structures snaps over the lips.